NOT APPLICABLE
NOT APPLICABLE
The following embodiments of the invention relate generally to integrated circuits. More particularly, these embodiments relate to micromachined (MEMS) devices.
In integrated circuits, it is common to provide various layers of material so as to fabricate the integrated circuit. This process is completed by depositing a passivation layer so as to protect the earlier deposited layers of materials. Furthermore, it is common to cap the integrated circuits with a plastic material to prevent their destruction. One type of integrated circuit, however, does not allow for such a passivation layer to be applied in view of the fact that the integrated circuit is comprised of an active mechanical component.
For example, in the field of micromachined (MEMS) devices, it is common to provide an active mechanical component, such as a mirror, that needs to be exposed to the atmosphere. In the case of a MEMS device that is comprised of mirrors, the mirrors need to be capable of receiving light transmission signals so that these transmission signals can be properly routed by reflection from the mirrors. Similarly, other components, for example, allow refraction or diffraction of various optical signals. These are merely examples, as MEMS devices can be comprised of other active mechanical components. Such MEMS devices make packaging of the integrated circuit components difficult in view of the fact that a passivation layer cannot be applied to the entire circuit when such active mechanical components must be free to move and receive signals.
One aspect of fabrication of integrated circuits is the deposition of material so as to form conductors that carry electrical signals throughout the integrated circuit. This is normally accomplished by depositing a conductive material that is suitable for conducting the particular electrical signal throughout the integrated circuit. One such conductive material is polysilicon which is conductive for purposes of transmitting digital signals in integrated circuits. Under normal circumstances, when a traditional integrated circuit is being fabricated, such a conductive material would be encapsulated by other materials and possibly a passivation layer so as to protect the conducting material from being exposed to extraneous particles which often occur as part of the fabrication process. In the manufacture of MEMS devices, however, the use of such encapsulating materials is not always possible, because the active mechanical components cannot be encapsulated without destroying their function. Thus, in packaging MEMS devices, it is sometimes necessary to deposit conductors which are exposed to the atmosphere and as a result can easily be shorted by the random particles which exist.
For example, such random particles can occur merely as dirt particles that exist in the atmosphere in which the integrated circuit is manufactured. Typically, such particles are filtered out of the processing environment through the use of stringent filtering controls; however, such filtering does not always catch every particle. Thus, some particles still make it though the filtering process and are capable of shorting out exposed conductors.
More typical, however, is that the manufacturing process itself results in fragments of silicon that are not completely removed during the various fabrication steps of a MEMS device. For example, the fabrication process is typically accomplished using deposition of successive layers of material along with intermediate removal of portions of these layers of material. Where these layers meet, it is typical to get fragments of material from the edges where other material has been removed. Silicon is very brittle, and therefore pieces of silicon at the edges where the layers of material meet can easily flake away resulting in free particles that drift to other portions of the circuit. These free particles are unintended; however, they are not that uncommon. Sometimes, these particles are referred to as xe2x80x9cstringersxe2x80x9d. Furthermore, stringers can result from sacrificial particles that are released during the fabrication process yet not entirely removed by a step of that process. For example, sometimes material can be intended to be etched away, yet merely broken free without removal from the integrated circuit. Therefore, this can result in the stringer being free to migrate to other portions of the circuit.
As a result of the presence of inherent dirt and stringers, these particles can cause the shorting out of a conductor during operation of the integrated circuit. MEMS devices are often different from the typical integrated circuit. Namely, MEMS devices often operate at very high voltages with a high density of exposed conductors in a given unit of the area of the circuit. In contrast, a typical integrated circuit, such as a memory device, often operates at very low voltages with conductors that are insulated from one another. Furthermore, such typical insulated integrated circuit devices usually do not have exposed wiring in the density that is common in MEMS devices. As a result, MEMS devices can be prone to shorting out as a result of the high voltages that exist and the proximity of exposed conductors operating at such a high potential difference. For example, such voltages can be in the hundreds of volts as compared to the five (5) volt signals, for example, used in some standard integrated circuit memory devices.
Thus, there is a desire for a technique that would provide a reduction in the occurrence of damage to MEMS devices which is brought about, for example, by electrical shorting.
One embodiment of the invention provides a method and apparatus for reducing the occurrence of damage caused by extraneous particles in integrated circuits. According to this embodiment of the invention, a substrate is provided for a micromachined device; a conductor is provided as part of the micromachined device for use in conducting electrical signals during operation of the micromachined device; and, a protective covering is provided for the conductor so that the conductor is disposed between the substrate and protective covering.
According to another embodiment of the invention, a micromachined apparatus can be fabricated comprising a substrate; a bonding pad; a conductor disposed over the substrate; wherein the conductor is electrically coupled with the bonding pad; an active mechanical component disposed over the substrate, wherein the active mechanical component is configured to move relative to the substrate; and a protective cover disposed over the conductor so that the conductor is disposed between the protective cover and the substrate.
According to another embodiment of the invention, a protective covering can be configured for a conductor by depositing a layer of material over the conductor so as to form a tunnel at least partially around the conductor. Thus the majority of the conductor can be protected from electrical shorts through the use of the tunnel which covers the majority length of the conductor.
According to another embodiment of the invention, a ground ring can be established about a conductor. Such a ground ring can be accomplished by electrically coupling a conductive material with the substrate of the circuit so as to provide an equipotential material as a protective cover for the conductor. Thus, for example, the equipotential surface can serve to isolate the conductor from stringers which migrate throughout the circuit.
Further embodiments of the invention will be apparent to those of ordinary skill in the art from a consideration of the following description taken in conjunction with the accompanying drawings, wherein certain methods, apparatuses, and articles of manufacture for practicing the embodiments of the invention are illustrated. However, it is to be understood that the invention is not limited to the details disclosed but includes all such variations and modifications as fall within the spirit of the invention and the scope of the appended claims.